If you train a muscle ED it's like endurance training for say a Decathelon... You'll build strength and endurance but you won't be doing yourself any good on building size. The fast-twitch or red muscle fibres need stimulation and then recovery to maxmize growth. Most of the bulking ability of your skeletal muscle comes from growing these red/fast-twitch fibres. The white/slow-twitch fibres don't respond to training with a size-response like the red/fast-twitch ones do. These white fibres respond with strength and endurance. Now, calves, abs, forearms just so happen to contain a higher percentage of the white fibres in them. So that's why you hear of guys training those parts ED. But, like Napalm and sully already said, you're over doing it if muscle growth is your goal.